Electrothermographic reproduction process



Sept. 7, 1965 M. GLOS ETAL ELECTRO'I'HERMOGRAPHIC REPRODUCTION PROCESS Filed Jan. 5, 1962 INVENTORS )Wmfln 6103 BY Erwin Lina ATT IVE) United States Patent 3,205,354 ELECTROTHERMOGRAPHIC REPRODUCTION PROCES Martin Glos, Wiesbaden, and Erwin Lind, Wiesbaden- Biebrich, Germany, assignors, by mesne assignments,

to Azoplate Corporation, Murray Hill, NJ.

Filed Jan. 5, 1962, Ser. No. 164,585 Claims priority, application Germany, Jan. 25, 1961,

K 42,669 7 Claims. (Cl. 250-65) The term electrothermography is applied to a reproduction process in which charge images are produced on an electrostatically charged layer by means of the action of heat. A resin layer, which may be supported on a material having adequate electrical conductivity and the specific resistance of which is reduced under the influence of heat, is electrostatically charged by a corona discharge. The original which is to be duplicated is placed on the thin, charged resin layer. The copying material thus arranged is then exposed, with the master in front, to infra-red radiation. In the dark parts of the master the incident infra-red rays are absorbed and converted into perceptible heat. As the master is in intimate contact with the charged resin layer, the heat from those parts of the master which absorb the heat rays is transferred to the resin layer by heat conduction. The resin layer therefore becomes hot in those parts which are under the heat-absorbing parts.

If a resin powder with a charge of the opposite polarity to that of the layer is used, a negative image of the master is obtained.

A n electrothermographic reproduction process has now been found in which an electrothermographic material with extensive heat-ray transmission is placed in such a manner on the master to be copied that the side of the copying material which is away from the master has an electrothermographic layer which is provided with an electrostatic charge, at the latest after the material has been put in place. Heat rays are then caused to act on the master through the electrothermographic material and the electrostatic image of the master thus obtained is developed andfixed in known manner. Alternatively, an unsupported electrothermographic layer can be employed in a similar manner.

For this process, suitable electrothermographic materials are primarly those comprising heat-sensitive layers which transmit heat rays so that the greatest possible part of the heat striking the layer passes through it and reaches the surface of the master which is to be copied. Accordingly, electrothermographic layers consisting in part or wholly of organic materials are primarily used, e.g., materials consisting of polyesters of terephthalic acid, isophthalic acid and ethylene glycol, chlorinated polyvinyl chloride, polyvinyl chloride, polyvinyl acetate, interpolymers from vinyl chloride and butadiene, polystyrene, interpolymers from vinyl chloride and vinyl acetate, chlorinated rubber, maleinate resins, ketone resins, colophony, pentaerythrite ester, phthalate resins, coumarone resins, and dimerized abietic acid.

As a support, a material which has a low absorption for heat rays may also be used. Primarily, cellulose products such as paper, cellulose hydrate foils, cellulose acetate, and cellulose acetobutyrate, also plastics such as polyesters,

polyamides, polyurethanes, polycarbonate and polyvinyl compounds are employed.

In performing the process, the electrothermographic material is placed on the master which is to be copied, the electrothermographic layer being on the side away from the master, in those cases where a support is used. The electrothermographic reproduction layer is previously provided with an electrostatic charge or, alternatively, it can be charged in the normal manner by means of a corona discharge after being placed on the master. Heat rays are then beamed upon the electrothermographic layer; they pass practically unimpeded through the electrostatically charged reproduction layer and its supporting material, if any, e.g., paper, and are absorbed in the image parts of the master. The absorbed heat is conducted from the image parts of the master through the supporting material, if any, of the electrothermographic reproduction material to the charged layer, which consequently becomes discharged in the image parts. Thus, an electrostatic charge image, which is a negative of the master, is formed. This is developed, to give a copy corresponding to the original, by dusting over with a suitable pigmented resin powder which has a charge of the same polarity as that of the electrostatic charge image. By means of this procedure, it is possible for non-reversed, directly readable copies to be produced from masters with printing or writing on one' or both sides The invention will be further illustrated by reference to the accompanying drawing which is a diagrammatic showing of the process of the present invention.

Referring to the drawing, an electrothermographic layer 1 on a suitable support 2 may be electrostatically charged by means of a corona discharge 4 either prior to or after being positioned adjacent a master 3. The electrothermographic layer and support, positioned adjacent the master, is then irradiated by exposure to a suitable infra-red radiation source 5, the heat rays passing through the electrostatically charged electrothermographic layer 1 to the master 3. After exposure, the master 3 is separated from the electrothermographic layer on the support and the latent image on the electrothermographic layer 1 is developed and fixed, resulting in a copy having a fixed visible image 6 thereon.

Because of the curling which tends to occur with thin papers having layers on one side only, it is advisable that the back of the reproduction material also be provided with a resin layer. For the back layer, the same resin as that used for the reproduction layer may be advantageously employed. In this way, a material which lies absolutely flat and which can be used on either side for the prepartion of electrothermographic copies is obtained. For charging, the reproduction material is placed on a grounded plate and charged by means of a corona dis charge, so that the two sides of the reproduction material take on electrostatic charges of opposite polarity. In order to obtain perfect copies it is advantageous for the supporting material selected to be sufficiently thin so that the heat coming from the original can be readily transferred by conduction. It is therefore advisable for the thickness of the heat-ray transmitting supporting material to be in the range of about 10 to preferably between about 20 to 60,14.

In the case of self-supporting foils or films, a thickness. in the range of about 1011. to p, preferably about 20 to 100p is employed.

The process of the invention enables directly read-able copies to be prepared in a simple manner by electrothermography from documents which can not be traced.

The invention will be further illustrated by reference to the following specific examples:

Example I 25 parts by weight of a mixed ester from terephthalic acid (70 percent) and isophthalic acid (30 percent) with ethylene glycol are dissolved in 200 parts by volume of chloroform. This solution is mechanically coated upon a thin transparent paper of a weight of 40 g. per square meter. The layer on the paper is positively charged by a corona discharge to a surface potential of 400 volts and [is then placed on an original with the layer side facing away from the original. The side of the material carrying the electrostatic charge is then exposed to an intensive heat source, e.g., a 1350-watt infra-red radiator. A non-reversed charge image, that is negative with respect to the master, is formed on the synthetic resin layer. This is made visible by treatment with a developer consisting of, e.g., 1 parts by weight of glass balls of a particle size of 300 to 400 and 2.5 parts by weight of a resin powder of a particle size 20 to 50p. The resin powder is obtained by melting together 30 parts by weight of polystyrene, 30 parts by weight of resin-modified maleic acid resin (Beckacite K105) and 3 parts by Weight of carbon black (Peerless Black Russ 552); the melt is then ground and screened.

Example 11 A thin, transparent paper of a weight of 40 g. per square meter is coated on both sides with a solution of 15 parts by weight of a chlorinated polyvinyl chloride in 200 parts by volume of toluene, the coating thickness on either side being about 10 By means of .a corona charging device, the material having a layer on either side is electrostatically charged. The upper side, which is .facing the corona, has a positive surface potential of 300 Volts; the lower side, which is away from the corona and lies on a grounded plate, has a negative surface potential of about 300 volts.

The electrostatically charged reproduction material is now placed on an original and the side that is away from the original is exposed to infra-red radiation. A nonreversed charge image, which is negative with respect to the original, is formed on the side that is away from the master. This can be made visible in known manner by powdering over with the developer described in Example I and fixed.

The material with a layer on both sides permits a negative or a positive image to be obtained using the same developer, depending upon which side of the charged paper is placed against the master.

Example III A foil of a thickness of 25;, made of a polyester of terephthal-ic acid and ethylene glycol, is placed on an original that is to be copied and is provided with a positive electrostatic charge by means of a corona discharge, so that the surface potential is about 400 volts above ground. The charged copying material is passed, together with the original, through the projection plane of a focused 1350-watt infra-red radiator so that the infrared radiation first penetrates the thin polyester foil and is then absorbed in the text parts of the original. The sensible heat formed in these parts as a result of the absorption is conducted back through the foil to the charged surface and a negative electrostatic charge image of the original is formed there. It is treated in known manner with a developer consisting of 100 parts by weight of glass balls of a grain size of 300 40011. and 0.5 part by weight of a resin powder of a grain size of -50 The resin powder is obtained by the melting together of 30 parts by weight of polystyrene, 30 parts by weight of resin-modified maleic acid resin and 3 parts by weight of carbon black, after which the melt is ground and screened.

4- The powder image corresponding to the original is fixed by a brief exposure to ethyl acetate vapor. The copy can be used for duplication purposes by the diazo process.

Example IV A foil of a thickness of approximately 50,41. made of a chlorinated polyvinyl chloride, obtained by a casting process in which a 10% benzene solution of the polymer is cast on a metal or glass plate, is placed uncharged upon an original which is to be copied. The surface of the toil which is remote from the original is then positively charged by means of a corona discharge to a surface potential of 300 volts above ground and is then subjected to a brief but intensive infra-red radiation and on this side of the foil, a negative non-reversed electrostatic charge image of the original is formed. This is made visible in known manner, using the developer described in Example III, and fixed by the action of solvent vapor.

Example V The procedure described in Example IV is followed but the negative laterally reversed electrostatic charge image formed on the side of the foil facing the original is made visible using the toner described in Example III. A laterally reversed negative image of the master is formed.

This application is a cont-inuation-in-part of application Serial Number 87,554, filed on February 7, 1961, now abandoned.

It will be obvious to those skilled in the art that many modifications may be made within the scope of the present invention without departing from the spirit thereof, and the invention includes all such modifications.

What is claimed is:

1. A photographic reproduction process which comprises directly exposing an electrostatically charged electrothermographic layer to heat rays while positioned adjacent a master, the heat rays being transmitted through the layer to the master, and developing the resulting image with an electrosoopic material.

2. A process according to claim 1 in which the layer is on one side only of a support.

3. A process according to claim 1 in which the layer is on both sides of a support.

4. A process according to claim 1 in which the layer is self-supporting.

5. A process according to claim 1 in which the layer is charged prior to being positioned adjacent the master.

6. A process according to claim 1 in which the layer is charged after being positioned adjacent the master.

7. A process according to claim 1 in which the layer is supported and exposed to heat with the layer facing away from the master.

References Cited by the Examiner UNITED STATES PATENTS 2,297,691 10/42 Carlson 250- X 2,573,881 11/51 Walkup et a1 25065 X 2,798,959 7/57 MoncrietT-Yeates 25065 2,808,777 10/57 Roshkind 250-65 X 2,844,733 7/58 Miller 250-65 2,914,403 11/59 Sugarman 250-65 X 2,970,906 2/61 Bixby 25065 X OTHER REFERENCES ElectrothcrmographyA New Electrostatic Printing Technique, by P. M. Cassiers, Photographic Science and Engineering, vol. 4, No. 4, July-August 1960.

RALPH G. NILSON, Primary Examiner.

'UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No 3 205,354 September 7, 1965 Martin Glos et a1.

It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

In the heading to the printed specification, lines 8 and 9, for "Claims priority, application Germany, Jan. 25, 1961,

K 42,669" read Claims priority, application Germany, Feb. 13, 1960, K 39,1597; Jan. 25, 1961, K 42,669

Signed and sealed this 8th day of March 1966.

(SEAL) Attest:

ERNEST W. SWIDER EDWARD J. BRENNER Attesting Officer Commissioner of Patents 

1. A PHOTOGRAPHIC REPRODUCTION PROCESS WHICH COMPRISES DIRECTLY EXPOSING AN ELECTROSTATICALLY CHARGED ELECTROTHERMOGRAPHIC LAYER TO HEAT RAYS WHILE POSITIONED ADJACENT A MASTER, THE HEAT RAYS BEING TRANSMITTED THROUGH THE LAYER TO THE MASTER, AND DEVELOPING THE RESULTING IMAGC WITH AN ELECTROSCOPIC MATERIAL. 